Auto thermal cracking reactor

ABSTRACT

The present invention provides a reactor design that enables an auto-thermal cracking process to be conducted at any suitable pressure wherein the gaseous reactants are preheated separately before mixing and then presented to the reaction zone in a uniformly distributed manner. In particular, the present invention-relates to apparatus for reacting a first and second gaseous reactant to form a gaseous product wherein the apparatus comprises at least one first supply means for the first gaseous reactant, at least one second supply means for the second gaseous reactant, a resistance zone and a reaction zone, preferably comprising a catalyst, wherein the first supply means comprises a plurality of first outlets for delivery of the first gaseous reactant, and the second supply means comprises a plurality of second outlets for delivery of the second gaseous reactant, the resistance zone is porous, the reaction zone is positioned downstream of the resistance zone with respect to the flow of the first and second gaseous reactants and wherein the first supply means and the second supply means are arranged such that the first gas and the second gas are contacted in an essentially parallel manner and mixed prior to contacting the resistance zone. The present invention also provides a process for the production of a mono-olefin utilizing said apparatus.

The present invention relates to a reactor suitable for the productionof olefins by auto-thermal cracking.

Auto-thermal cracking is a known process for the production of olefins.An example of such a process is described in EP-A-0 332 289. In thisprocess, a hydrocarbon and an oxygen-containing gas are contacted with acatalyst, which is capable of supporting combustion beyond the fuel richlimit of flammability. The hydrocarbon is partially combusted, and theheat produced is used to drive the dehydrogenation of the hydrocarbonfeed into olefins.

In the auto-thermal cracking process the hydrocarbon and theoxygen-containing gas may be uniformly mixed and preheated prior tocontacting the catalyst. However mixing and preheating the hydrocarbonand oxygen-containing gas becomes problematic if it is desired to carryout the process at elevated pressure due to flammability constraints.Thus, it becomes desirable to reduce the time between forming themixture of hot gaseous reactants and contacting the mixture with thecatalyst.

The present invention provides a reactor design that enables anauto-thermal cracking process to be conducted at any suitable pressurewherein the gaseous reactants are preheated separately before mixing andthen presented to the reaction zone in a uniformly distributed manner.

Accordingly the present invention provides apparatus for reacting afirst gaseous reactant with a second gaseous reactant to form a gaseousproduct, wherein the apparatus comprises at least one first supply meansfor the first gaseous reactant, at least one second supply means for thesecond gaseous reactant, a resistance zone and a reaction zone,preferably comprising a catalyst, and

wherein the first supply means comprises a plurality of first outletsfor delivery of the first gaseous reactant, and the second supply meanscomprises a plurality of second outlets for delivery of the secondgaseous reactant,

the resistance zone is porous, is positioned downstream of the first andsecond supply means with respect to the flow of the first and secondgaseous reactants and is in fluid communication with the first andsecond supply means,

the reaction zone is positioned downstream of the resistance zone withrespect to the flow of the first and second gaseous reactants and is influid communication with the resistance zone, and

wherein the first supply means and the second supply means are arrangedsuch that the first gas and the second gas are contacted in anessentially parallel manner and mixed prior to contacting the resistancezone.

Preferably, the first supply means comprises at least one first inletfor supplying a first gaseous reactant to at least one first manifoldand a plurality of first outlets exiting the first manifold for deliveryof the first gaseous reactant, and the second supply means comprises atleast one second inlet for supplying a second gaseous reactant to atleast one second manifold and a plurality of second outlets exiting thesecond manifold for delivery of the second gaseous reactant.

The apparatus suitably comprises at least 100, preferably at least 500,most preferably at least 1000, first and second outlets per metresquared of the transverse cross section of the reaction zone.

The first and second supply means are arranged such that the first andsecond gas are contacted in an essentially parallel manner. By“essentially parallel manner” is meant that the first and second gas,when they are brought into contact, are both flowing in essentially thesame direction, such as axially, rather than flowing in opposite ortangential relative directions. Contacting the gases in an essentiallyparallel manner, rather than, for example, in a tangential manner,provides reduced turbulence in the region where the gases first contact(where mixing is not yet complete, and the compositions of gases presentcan vary significantly).

Turbulence can increase the residence time of mixed gas in the reactor,which increases the risk of flammability problems arising. In somecases, contacting the gases in a perpendicular manner can lead toregions of low flow, or even stagnant regions, containing flammable gasmixtures close to the contacting region. Contacting the gases in anessentially parallel manner according to the present invention reducesthe potential for regions of low flow mixed gas, reducing the potentialfor flammability problems.

In a first embodiment of the invention the contacting/mixing arrangementis provided by positioning one supply means within the other andproviding at least a portion of the supply means located within theother with suitable openings such that one gaseous reactant can passthrough the openings and contact the other gaseous reactant.

Preferably, the first embodiment of the invention provides apparatuswherein

the first supply means comprises at least one first inlet for supplyinga first gaseous reactant to at least one first manifold and a pluralityof injection tubes exiting said first manifold for delivery of the firstgaseous reactant, and the second supply means comprises at least onesecond inlet for supplying a second gaseous reactant to at least onesecond manifold and a plurality of conduits exiting said second manifoldfor delivery of the second gaseous reactant,

wherein the second manifold is positioned downstream of the firstmanifold with respect to the flow of the first gaseous reactant,

the resistance zone is porous, is positioned downstream of the secondmanifold with respect to the flow of the first and second gaseousreactants and is in fluid communication with the conduits exiting thesecond manifold,

the reaction zone is positioned downstream of the resistance zone withrespect to the flow of the first and second gaseous reactants and is influid communication with the resistance zone, and

wherein each conduit comprises an upstream end exiting the secondmanifold and a downstream end in fluid communication with the resistancezone and wherein the injection tubes exiting the first manifold arearranged such that they extend through the second manifold and projectaxially into the upstream end of the conduits.

Advantageously the apparatus of the first embodiment usually comprises afirst cooling zone contacting the downstream end of the plurality ofconduits exiting the second manifold arranged such that the downstreamend of the plurality of conduits are cooled. This ensures that thegaseous reactants are prevented from reacting until they enter thereaction zone.

Furthermore the apparatus of the first embodiment usually comprises aproduct cooling zone downstream of the reaction zone such that thegaseous products can be cooled upon exiting the reaction zone.

In the first embodiment of the invention, preferably, the first manifoldis a first chamber and the second manifold is a second chamber and theinjection tubes exiting the first chamber form a plurality of elongatedpassageways extending through the second chamber into the upstream endof the plurality of conduits exiting the second manifold.

The volumes of the first and second chambers are not especiallycritical. However, in a preferred embodiment, the volumes of the firstand second chambers are adapted to be relatively small for safetyreasons. Typically when the reactor diameter is 600 mm the volume of thefirst chamber is usually between 5-100 litres, preferably: between 10-40litres and more preferably between 15-25 litres e.g. 22 litres. Thevolume of these chambers will be proportional to the cross-sectionalarea of the reactor (i.e. diameter squared)

Typically when the reactor diameter is 600 mm the volume of the secondchamber is usually between 20-200 litres, preferably between 30-100litres and more preferably between 40-80 litres e.g. 50 litres.

The apparatus of the first embodiment usually comprises an equal numberof injection tubes and conduits, each injection tube projecting into acorresponding conduit. Preferably the apparatus comprises at least 100,preferably at least 500, most preferably at least 1000 injection tubesper metre squared of the transverse cross section of the reaction zone.

So as to allow the injection tubes to project into the conduits theexternal diameter of the injection tubes where they project into theconduits is less than the internal diameter of the conduits. The exactexternal diameter is not critical to the invention, but usually theinjection tubes have an external diameter of between 2.0 to 5.0 mm, e.g.4.0 mm. The injection tubes have a length sufficient to extend throughthe second chamber (i.e. typically greater than 170 mm).

At the end of each of the plurality of injection tubes remote from themanifold, the first gaseous reactant can exit the tubes through asuitable opening, preferably a nozzle, and which has a diameter lessthan the external diameter of the injection tube, preferably between 0.5to 3.0 mm, such as between 1.0 to 2.0 mm. The nozzle, when present,preferably has a diameter less than the internal diameter of theinjection tube other than at the nozzle, hence providing a restrictionthat assists in obtaining even flow rates from all injection tubes,without providing the pressure drop characteristics that would beobtained if the internal diameter of the injection tube was this sizefor a significant length of the injection tube.

Usually the conduits have an internal diameter of between 1 to 10 mm,preferably between 2 to 8 mm e.g. 7 mm and a length of between 50 to 500mm, preferably between 100 to 300 mm e.g. 210 mm. The conduits may bearranged in a symmetrical configuration such as in a triangular orsquare configuration.

The ratio of the inner diameter of the conduits to the diameter of theopening, e.g. nozzle, of the injection tubes is suitably in the range2:1 to 10:1, for example, in the range 3:1 to 5:1.

Where the injection tubes of the first supply means extend through themanifold of the second supply means, each injection tube may be providedwith an outer tube, around the injection tube (which forms an inner tubewithin said outer tube). The outer tube provides thermal insulation fromthe second gaseous reactant when this is at a different temperature thanthe first gaseous reactant (which passes along the inside of the innertube).

In a further preferred embodiment, suitable flow restrictors are alsoprovided between the outer surface of the injection tubes and the innersurface of the conduits, at a location at or close to where theinjection tubes enter the conduits at the upstream end of the conduits(i.e. close to the second manifold). These flow restrictors may belocated on the injection tubes and/or on the conduits, and, by providingresistance, they assist in obtaining even flow rates of the secondgaseous reactant into each conduit. These flow restrictors should belocated remote from the exits of the first injection tubes such that thevelocity of the second gaseous reactant, which has a maximum velocity inthe conduit when passing through or past the flow restrictors, hasreduced (from that maximum) when mixed with the first gaseous reactant.Preferably the pressure drop of the flow passing these restrictions isof similar order as the pressure drop of the first gaseous reactantthrough the nozzles or other restrictions at the end of the injectiontubes (such as 1 bar and 0.5 bar respectively). This ensures that theproportions of the reactants entering the reaction zone remain similarwhen there are small fluctuations in pressures in the reaction zone orin the feeds. For optimum yields, the tolerance on the nozzle diametersand the flow restrictors for the second gaseous reactant should be suchthat the concentration of the gaseous mixture varies by no more than 5%.

Typically, between 5-40 mm, preferably between 10-30 mm, and mostpreferably between 15-25 mm e.g. 20 mm of the length of the injectiontube projects axially into the conduit.

Wherein the apparatus of the first embodiment comprises a first coolingzone the first cooling zone is preferably provided by contacting acooling fluid with the external surface area of the downstream end ofthe conduits. Typically, 10-20% of the external surface area of theconduit may be contacted with the cooling fluid.

In a second embodiment of the present invention, the contacting/mixingarrangement is provided by a first supply means comprising at least onefirst inlet for supplying a first gaseous reactant to at least one firstmanifold and a plurality of first injection tubes exiting said firstmanifold for delivery of the first gaseous reactant, and a second supplymeans comprising at least one second inlet for supplying a secondgaseous reactant to at least one second manifold and a plurality ofsecond injection tubes exiting said second manifold for delivery of thesecond gaseous reactant, wherein each injection tube has an exit at theend remote from the manifold and which has a cross-sectional opening of1 mm² or less, and wherein the exits from the first and second injectiontubes are in an intermixed configuration.

By intermixed, as used herein, is meant that the exits of the pluralityof first injection tubes are dispersed amongst the exits of theplurality of second injection tubes and/or vice versa. Thus, forexample, where there are more first injection tubes than secondinjection tubes, the exits of the second injection tubes will bedispersed amongst the exits of the first injection tubes and the optimalconfiguration for the exits for the second injection tubes will be suchthat each second injection tube will have the exit of at least one firstinjection tube as its nearest neighbour.

Suitably, there are at least 10000 first and second injection tubes intotal per square metre. The use of said number of intermixed tubesprovides rapid mixing at the outlets of said tubes.

For optimal delivery of the first and second gaseous reactants to theresistance zone, the exits from the injection tubes of the secondembodiment should all be located in an essentially planar configuration.

The exits of the first injection tubes may be arranged in a symmetricalconfiguration, such as in a triangular, square, rectangular or hexagonalconfiguration and/or the exits of the second injection tubes may bearranged in a symmetrical configuration, such as in a triangular,square, rectangular or hexagonal configuration.

In this second embodiment, the exits may be any suitable shape incross-section, such as triangular, rectangular, square, hexagonal,D-shaped, oval or circular.

Mixing of the gases becomes more rapid as the number of tubes isincreased and the cross-sectional opening of the exits of the tubes isdecreased.

Thus in a preferred aspect of the second embodiment of the presentinvention, each injection tube has an exit at the end remote from themanifold which has a cross-sectional opening of 0.5 mm² or less. Morepreferably the exits have a cross-sectional opening of 0.2 mm² or less,such as 0.1 mm² or less. Suitably, the exits have a cross-sectionalopening of 0.004 mm² or more.

The exits for the injection tubes for one reactant may vary in size andshape but are preferably the same. Similarly, the exits for the secondgaseous reactant may be different to, or may be the same size and shapeas the exits for the first gaseous reactant.

Most preferably, the exits are D-shaped, such as semi-circular, with across-sectional opening of between 0.01 mm² and 0.05 mm².

The apparatus of this second embodiment may comprise an equal number offirst and second injection tubes for delivery of said first and secondgaseous reactants respectively. Alternatively, the relative number ofinjection tubes for delivery of each gaseous reactant may be different,for example, the relative number of injection tubes for delivery of eachgaseous reactant may be in proportion to the relative amount of eachgaseous reactant to be delivered. However, the relationship between thenumbers of tubes is not critical to the invention, and, for example, thevelocities of the first and second gaseous reactants exiting therespective injection tubes may be, and preferably are, different. Inparticular, the use of differing flow rates for each of the first andsecond gaseous reactants allows different ratios of said first andsecond gaseous reactants to be achieved utilizing a fixed number ofinjection tubes for each reactant.

Preferably, one of the reactants, more preferably the reactant withlowest molecular mass, exits one set of the injection tubes with ahigher velocity than the other reactant exits the other injection tubes.For example, the size and number of the injection tubes for one reactantmay be such that the ratio of the exit velocities is at least 10:1 forexample the exit velocity of one reactant is at least 100 m/s while thenumber and size of the injection tubes for the other reactant may besuch that the exit velocity is less than 10 m/s. The mean velocity ofthe combined flows having exited the injection tubes may be of the orderof 3 m/s.

As the cross-sectional opening of the exit tubes decreases, so thenumber of first and second injection tubes per unit area of thetransverse cross-section of the reaction zone can increase. Thus, theapparatus of the second embodiment may comprise at least 100000, forexample at least 1000000, such as 4000000 injection tubes (total offirst and second injection tubes) per square metre of the transversecross section of the reaction zone.

Similarly, the distance between one exit and its nearest neighbour willalso decrease as the cross-sectional opening of the exit tubes decreasesand the number of first and second injection tubes increases. Thus, thedistance between one exit and its nearest neighbour in this secondembodiment may be less than 2000 microns, such as less than 1000 micronsand preferably in the range 100 to 500 microns. The distance betweenneighbouring tubes is preferably of similar dimension to the exitsthemselves, such as in the range from one half to twice the maximumdimension across the opening of the exit.

By using the intermixed arrangement of the first and second injectiontubes with relatively small exit holes according to the secondembodiment of the present invention, for delivery of the first andsecond gaseous reactants respectively, rapid mixing of the first andsecond gaseous reactants is achieved. Typically, by using an intermixedarrangement of the first and second injection tubes with exits with across-sectional opening of 0.5 mm² or less, adequate mixing may beachieved in a distance of less than 5 mm from the exits of the injectiontubes, allowing the gases to be mixed and contacted with the resistancezone in a short space, and, hence, within a short period of time.

The apparatus of the second embodiment usually comprises a productcooling zone downstream of the reaction zone, such that the gaseousproducts can be cooled upon exiting the reaction zone.

Preferably, in the second embodiment of the invention, the firstmanifold comprises a first chamber and the second manifold comprises asecond chamber, with the respective first and second gaseous componentsexiting therefrom and into a plurality of first and second injectiontubes. The injection tubes with exits with a cross-sectional opening of1 mm² or less are preferably formed as passageways in a diffusion bondedblock. Diffusion bonded blocks formed by diffusion bonding of layers ofetched metal structures are known for heat exchange uses, and aredescribed generally, for example, in “Industrial MicrochannelDevices—Where are We Today?”; Pua, L. M. and Rumbold, S. O.; FirstInternational Conferences on Microchannels and Minichannels, Rochester,N.Y., April 2003.

The use of diffusion bonding techniques in the present invention allowsa plurality of passageways to be formed connecting the first and secondchambers respectively to a plurality of first and second exits, theexits being in an intermixed configuration, as required for forming theinjection tubes of the second embodiment of the present invention.

As with the first embodiment, the volume of the first and secondchambers are not especially critical, but, preferably, the volume of thefirst and second chambers in the second embodiment are adapted to berelatively small for safety reasons.

After mixing according to the process of the present invention, eitherby the apparatus of the first or second embodiment, or otherwise, themixed first and second gaseous reactants are contacted with a resistancezone positioned downstream of first and second supply means.

The resistance zone is porous. The permeability of the porous resistancezone ensures dispersion of the fluid reactants as they pass through thezone. The fluids move through a network of channels laterally as well asaxially (axially being the general direction of flow of the reactantsthrough the resistance zone), and leave the resistance zonesubstantially uniformly distributed over the cross-sectional area of theresistance zone.

Preferably, the resistance zone is as permeable laterally as it isaxially. More preferably the resistance zone has a permeability which issubstantially the same in any direction, such as having a permeabilityin any direction which is from 0.2 to 5 times the permeability in anyother direction.

Methods are known for determining the permeability of porous media. Thepressure gradient or pressure drop per unit length through theresistance zone may be defined using the inertial resistance coefficientwhere the pressure gradient equals the product of the inertialresistance coefficient and the dynamic pressure. The dynamic pressure ishalf the product of the fluid density and the square of the superficialvelocity and has units of pressure. The inertial resistance coefficienthas units of reciprocal length. The resistance zone usually has anaverage inertial resistance coefficient (i.e. averaged over alldirections) of between 500-10000/metre (/m), preferably between2000-4000/m and advantageously between 2500-3500/m e.g. 3250/m.

The resistance zone may be formed of a porous metal structure, butpreferably the porous material is a non metal e.g. a ceramic material.Suitable ceramic materials include lithium aluminium silicate (LAS),alumina (αAl₂O₃), yttria stabilised zirconia, alumina titanate, niascon,and calcium zirconyl phosphate. A preferred porous material is gammaalumina.

The distance of the resistance zone from the ends of the conduits in thefirst embodiment and the exit of the tubes in the second embodiment ispreferably less than 20 mm, more preferably between 1 and 10 mm, morepreferably between 1.5 and 5 mm, such as 2 mm.

Wherein the reaction zone comprises a supported catalyst preferably theporous material in the resistance zone may be the same as the porousmaterial used as the catalyst support. The porous material may be in theform of spheres, other granular shapes or ceramic foams. The reactionzone may comprise a supported catalyst in the form of a monolithproviding a continuous multichannel structure.

For the porous material in the resistance zone, advantageously at least70%, preferably at least 80% and advantageously at least 90% of thepores have a pore width of less than 5.0 mm e.g. usually between 0.1-3.0mm, preferably between 0.2-2.0 mm and most preferably between 0.5-1.5mm.

Typically the resistance zone has between 10-60 pores per square inch,preferably between 20-50 pores per square inch and most preferablybetween 30-45 pores per square inch.

Usually the depth of the resistance zone is between 5-100 mm but ispreferably 10-50 mm.

Usually the reaction zone has a depth of between 10-200 mm but ispreferably 20-100 mm e.g. 60 mm. Preferably the reaction zone comprisesa catalyst.

(The depth of the resistance zone and the reaction zone are measured inthe direction of flow of the reactant gases. In general, the preferreddepths are defined by the flow rate of the reactant gases, since thisdetermines the contact time, and, as with other dimensions measured inthe direction of gas flow, are, for most practical purposes, independentof reactor cross-section.)

When a catalyst is employed suitably the catalyst is a supportedplatinum group metal. Preferably, the metal is either platinum orpalladium, or a mixture thereof. Although a wide range of supportmaterials are available, it is preferred to use alumina as the support.The support material may be in the form of spheres, other granularshapes or ceramic foams. Preferably, the support is a monolith which isa continuous multichannel ceramic structure, frequently of a honeycombappearance. A preferred support for the catalytically active metals is agamma alumina. The support is loaded with a mixture of platinum andpalladium by conventional methods well known to those skilled in theart. The resulting compound is then heat treated to 1200° C. before use.catalyst promoters may also be loaded onto the support. Suitablepromoters include copper and tin.

The catalyst is usually held in place in the reactor in a suitableholder, such as a catalyst basket. Preferably, to prevent gas by-passingthe catalyst between the catalyst and the holder, any space between thecatalyst and the holder is filled with a suitable sealing material.Suitable sealing materials include man made mineral wools e.g. ceramicwool, which can be wrapped around the edges of the catalyst in theholder. In addition the catalyst may be coated around the edge with amaterial similar to the main catalyst support material, such as alumina,to aid this sealing.

The apparatus may comprise a product cooling zone downstream of thereaction zone, such that the gaseous products can be cooled upon exitingthe reaction zone. The product cooling zone may be provided by one ormore injection nozzles that are capable of injecting a condensate intothe product stream exiting the reaction zone.

Preferably the first and second manifolds, the injection tubes, theconduits (if present), the housing for the resistance zone and thereaction zone are metallic e.g. steel. Where pure oxygen is employed asa gaseous reactant it may be necessary to make or coat some or all ofany part of the apparatus that may contact the oxygen from/with an alloythat resists reaction with oxygen. Reaction with oxygen is more likelywhen the temperature of the oxygen is high and/or the oxygen is at highvelocity. Suitable alloys include monel.

Immediately downstream of the reaction zone, where the temperature ofthe products from the reaction is high, the preferred material ofconstruction is a high nickel alloy, such as Inconel, Incaloy, Hastelloyor Paralloy. The metal may be formed into shape by one or more of thefollowing techniques: static casting, rotational casting, forging,machining and welding.

The apparatus may comprise a suitable thermal sleeve to reduce thermalstresses on the apparatus immediately downstream of the reaction zone.Thermal stresses can occur where relatively rapid changes intemperature, either a rapid increase or decrease, occur inside anapparatus, for example, at start-up or shut-down. The inner surface ofthe wall of the apparatus heats or cools rapidly, but the outer surfaceheats or cools more slowly providing stress across the wall (the wallbeing relatively thick, for example, to cope with the pressuredifferential between the inside of and the outside of the apparatus).The use of a sleeve of thin material, which may be of a similar materialto the wall of the apparatus, as a thermal sleeve inside the apparatusreduces the rate of temperature change that impacts the inner surface ofthe wall, and hence reduces the thermal stress.

The apparatus is advantageously employed to partially oxidize a gaseousfeedstock. Preferably the first gaseous reactant is an oxygen containinggas and the second gaseous reactant is a gaseous paraffinic hydrocarbon.

The present invention also provides a process for the production of amono-olefin utilizing the apparatus previously described.

Thus, utilizing the apparatus of the first embodiment, the inventionprovides a process for the production of a mono-olefin said processcomprising passing an oxygen containing gas into a first manifold andinjecting the oxygen-containing gas via a plurality of injection tubesinto a plurality of conduits, passing gaseous paraffinic hydrocarbon viaa second manifold into the plurality of conduits wherein the gaseousparaffinic hydrocarbon is contacted in an essentially parallel mannerand mixed with the oxygen-containing gas, passing the gaseous mixture toa reaction zone via a porous resistance zone, and partially combustingin the reaction zone the gaseous mixture, preferably in the presence ofa catalyst which is capable of supporting combustion beyond the fuelrich limit of flammability, to produce the mono-olefin.

Utilizing the apparatus of the second embodiment, the invention providesa process for the production of a mono-olefin said process comprising

passing an oxygen containing gas from at least one first inlet via atleast one first manifold to a plurality of first injection tubes andpassing a gaseous paraffinic hydrocarbon from at least one second inletvia at least one second manifold to a plurality of second injectiontubes, wherein each injection tube has an exit at the end remote fromthe manifold and which has a cross-sectional opening of 1 mm² or less,and wherein the exits from the first and second injection tubes areco-located in an intermixed configuration,

passing the gaseous mixture to a reaction zone via a porous resistancezone, and partially combusting in the reaction zone the gaseous mixture,preferably in the presence of a catalyst which is capable of supportingcombustion beyond the fuel rich limit of flammability, to produce themono-olefin.

Preferred processes for the production of a mono-olefin utilizeapparatus with the preferred features as previously described. Thus, forexample, the preferred apparatus for a process utilizing the apparatusof the second embodiment is such that each injection tube has an exit atthe end remote from the manifold which has a cross-sectional opening of0.5 mm² or less. More preferably the exits have a cross-sectionalopening of 0.2 mm² or less, such as 0.1 mm² or less.

In the process for the production of a mono-olefin from a feedstockcomprising a gaseous paraffinic hydrocarbon, the paraffinic hydrocarbonmay suitably be ethane, propane or butane. The paraffinic hydrocarbonmaybe substantially pure or may be in admixture with other hydrocarbonsand optionally other materials, for example methane, nitrogen, carbonmonoxide, carbon dioxide, steam or hydrogen. A paraffinichydrocarbon-containing fraction such as naphtha, gas oil, vacuum gasoil, or mixtures thereof, may be employed. A suitable feedstock is amixture of gaseous paraffinic hydrocarbons, principally comprisingethane, resulting from the separation of methane from natural gas. Apreferred feedstock is a paraffinic hydrocarbon principally comprisingethane which provides a product principally comprising ethylene as themono-olefin.

As the oxygen-containing gas there may suitably be used either oxygen orair. It is preferred to use oxygen, optionally diluted with an inertgas, for example nitrogen. The ratio of the gaseous paraffinichydrocarbon to the oxygen-containing gas mixture is usually from 5 to 20times the stoichiometric ratio of hydrocarbon to oxygen-containing gasfor complete combustion to carbon dioxide and water. The preferredcomposition is from 5 to 10 times the stoichiometric ratio ofhydrocarbon to oxygen-containing gas.

Although the apparatus can be used at any pressure e.g. between 0-100barg it is particularly useful at elevated pressure. The pressure at thefirst and second inlets is preferably between 10-50 barg, mostpreferably between 20-40 barg, and advantageously between 25-35 barge.g. 30 barg.

The oxygen containing gas may be fed at ambient temperature, but isusually preheated to 50 to 150° C., preferably 80-120° C. e.g. 100° C.The oxygen containing gas is injected into the conduits or from theexits of the plurality of injection tubes at a velocity to prevent thepossibility of a flame stabilizing on the exits of the injection tubes.Especially in the first embodiment of the present invention, theinjection tubes may end in a suitable nozzle to increase the exitvelocity The exit velocity is typically greater than 30 m/s, preferablygreater than 50 m/s, and advantageously greater than 70 m/s.

The gaseous paraffinic hydrocarbon is usually preheated to 100 to 400°C., preferably 150-350° C. e.g. 300° C. and passed into the conduits orfrom the plurality of second injection tubes wherein it is intimatelymixed with the oxygen containing gas. The gaseous paraffinic hydrocarbonenters the conduits or exits the plurality of second injection tubes ata velocity typically greater than 5 m/s, preferably greater than 15 m/s,and advantageously greater than 20 m/s.

In the first embodiment, the velocity of the oxygen containing gasexiting the injection tubes and the velocity of the gaseous paraffinichydrocarbon passing into the conduits preferably has the ratio of atleast 1.5:1, preferably at least 3:1 and most preferably less than 6:1,such as 4:1. This ratio ensures rapid mixing.

In the second embodiment, the ratio of the velocity of the oxygencontaining gas exiting the first injection tubes and the velocity of thegaseous paraffinic hydrocarbon exiting the second injection tubes willdepend on the relative ratios of numbers of first and second injectiontubes, their relative sizes and the desired oxygen to paraffinichydrocarbon ratio, but preferably the ratio is at least 0.1:1,preferably at least 1:1 and most preferably at least 5:1. Typically, theexit velocity of the oxygen containing gas is at least 50 m/s,especially at least 100 m/s. For example, the size and number of theinjection tubes for the oxygen containing gas may be such that the exitvelocity is at least 100 m/s while the number and size of the injectiontubes for the gaseous paraffinic hydrocarbon may be such that the exitvelocity is less than 10 m/s, and the mean velocity of the combinedflows having exited the injection tubes maybe of the order of 3 m/s.

The temperature of the gaseous mixture is usually between 100 to 400°C., preferably 100 to 300° C. e.g. 200° C. In addition to passing thegaseous paraffinic hydrocarbon to the conduits or second injectiontubes, other gases may also be passed to the conduits or secondinjection tubes e.g. hydrogen, carbon monoxide and/or carbon dioxide.

In the first embodiment, the gas mixture may be cooled by the firstcooling zone wherein a coolant, such as water, is passed around theexternal surface area of the downstream end of the conduits; The coolingof the downstream end of the conduits prevents local heating of theconduit which eliminates the tendency for any “flame creep back” in theevent of a stable flame being formed at the exit of the conduits.

The temperature of the coolant is typically between 20-200° C., andpreferably between 80-120° C. e.g. 100° C. The coolant flow rate ismanipulated such that the coolant temperature increase is less than 100°C., preferably less than 50° C., and most preferably less than 30° C.

The first cooling zone reduces the temperature of the gaseous mixture byat least 10° C., preferably by at least 20° C., and most preferably byat least 30° C.

In both embodiments the gaseous mixture is usually passed to theresistance zone at a mean cross-section velocity between 1.0-10.0 m/s,preferably between 2.0-6.0 m/s and most preferably between 2.5-3.5 m/s.

The gaseous mixture is usually passed to the reaction zone at a velocitybetween 1.0-10.0 m/s, preferably between 2.0-6.0 m/s and most preferablybetween 2.5-3.5 m/s.

The pressure drop through the resistance zone is typically between0:01-0.2 bar, and preferably between 0.05-0.1 bar e.g. 0.08 bar.

The temperature in the reaction zone is usually greater than 500° C.,for example greater than 650° C., typically greater than 750° C., andpreferably greater than 800° C. The upper temperature limit may suitablybe up to 1200° C., for example up to 1100° C., preferably up to 1000° C.

The products exit the reaction zone at a temperature greater than 800°C. e.g. greater than 900° C. and at a pressure usually between 10-50barg, most preferably between 20-40 barg, and advantageously between25-35 barg e.g. 30 barg.

Preferably the products are rapidly cooled in a product cooling zone.This ensures a high olefinic yield because the product cooling stepslows down the rate of reaction in the gaseous product stream thuspreventing further reactions taking place.

Advantageously the gaseous product stream is cooled by injecting acondensate into the gaseous product stream, preferably at multiplepoints, such that the vaporisation of the condensate cools the gaseousproduct stream.

The condensate may be a gas or a liquid. When the condensate is gas itis preferably an inert gas. Preferably the condensate is a liquid e.g.water.

Injecting the condensate at high pressure and high temperature ensuresthat a large proportion of the condensate instantaneously vaporizes atthe reactor pressure and therefore provides a very rapid temperaturedrop in the gaseous product stream. Consequently the condensate, such aswater, is usually injected at a pressure higher than the pressure of thegaseous product stream, such as 100 barg and is usually injected at atemperature of between 100-400° C. and preferably between 200-350° C.e.g. 300° C.

Preferably the temperature of the gaseous product stream is reduced to800° C. preferably to 600° C. within 60 mS preferably 40 mS andadvantageously 20 mS from exiting the reaction zone.

The present invention will now be illustrated with the aid of figures,wherein:

FIG. 1 represents an apparatus according to the first embodiment of thepresent invention,

FIG. 2 a represents schematically a section of an intermixedconfiguration of first and second injection tubes for an apparatusaccording to the second embodiment of the present invention, and

FIG. 2 b represents schematically a side view of an apparatus accordingto the second embodiment of the present invention.

In FIG. 1 an oxygen containing gas is passed via a first inlet (1) intoa first chamber (2) and then into a plurality of injection tubes (3). Agaseous paraffinic hydrocarbon is passed via second inlet (4) into asecond chamber (5) and then into the plurality of conduits (6). Theoxygen containing gas is injected via injection tubes (3) into theconduits (6) wherein the gaseous paraffinic hydrocarbon is mixed withthe oxygen-containing gas.

The gaseous mixture is then passed to the resistance zone (7) whereinthe momentum is taken from the gaseous mixture such that it is passed ina uniform manner to the reaction zone (8) which comprises a catalystwhich is capable of supporting combustion beyond the fuel rich limit offlammability. The gaseous reactants are converted in the reaction zone(8) to provide a product stream comprising olefins.

Prior to passing the gaseous mixture to the resistance zone (7) a firstcooling zone (9) contacting the downstream end of the plurality ofconduits is used to reduce the temperature of the gaseous mixture.

Finally the product stream comprising olefins is passed to a productcooling zone (10) to reduce the temperature of the product stream priorto recovery.

In FIG. 2 a, a series of first injection tubes (23), shown by opencircles, are arranged in a triangular configuration. The exits of thefirst injection tubes are dispersed amongst the exits of a plurality ofsecond injection tubes (26), which are arranged in a rectangularconfiguration. In the overall arrangement (the Figure shows just asection) there are approximately twice as many second injection tubes asfirst injection tubes in this configuration.

In FIG. 2 b an oxygen containing gas is passed into a first chamber (22)and then into the plurality of first injection tubes (23). A gaseousparaffinic hydrocarbon is passed into a second chamber (25) and theninto the plurality of second injection tubes (26). The oxygen containinggas and gaseous paraffinic hydrocarbon exit the respective injectiontubes and rapidly mix.

The gaseous mixture is then passed to the resistance zone (27) whereinthe velocity of the gaseous mixture is smoothed (momentum is taken fromthe gaseous mixture) such that it is passed in a uniform manner to areaction zone (28) which comprises a catalyst which is capable ofsupporting combustion beyond the fuel rich limit of flammability. Thegaseous reactants are converted in the reaction zone (28) to provide aproduct stream comprising olefins.

Finally the product stream comprising olefins is passed to a productcooling zone (not shown) to reduce the temperature of the product streamprior to recovery.

1-21. (canceled)
 22. A process for the production of a mono-olefin byreacting an oxygen containing gas with a gaseous paraffinic hydrocarbonto form said mono-olefin, which process utilizes an apparatus whichcomprises a first supply means which comprises a plurality of firstoutlets for delivery of the oxygen containing gas, and a second supplymeans which comprises a plurality of second outlets for delivery of thegaseous paraffinic hydrocarbon, a resistance zone and a reaction zone,wherein the resistance zone is porous, is positioned downstream of thefirst and second supply means with respect to the flow of the oxygencontaining gas and the gaseous paraffinic hydrocarbon and is in fluidcommunication with the first and second supply means, the reaction zoneis positioned downstream of the resistance zone with respect to the flowof the oxygen containing gas and the gaseous paraffinic hydrocarbon andis fluid communication with the resistance zone, and wherein the firstsupply means and the second supply means are arranged such that thefirst gas and the second gas are contacted in an essentially parallelmanner and mixed prior to contacting the resistance zone, which processcomprises: passing oxygen containing gas into said first supply meansand passing gaseous paraffinic hydrocarbon into said second supplymeans, such that the gaseous paraffinic hydrocarbon is contacted in anessentially parallel manner and mixed with the oxygen-containing gas,passing the gaseous mixture to the reaction zone via the porousresistance zone and partially combusting the gaseous mixture in thereaction zone in the presence of a catalyst which is capable ofsupporting combustion beyond the fuel rich limit of flammability, toproduce the mono-olefin.
 23. The process according to claim 22, whereinthe apparatus comprises at least 100, preferably at least 500, mostpreferably at least 1000, first and second outlets per metre squared ofthe transverse cross section of the reaction zone.
 24. The processaccording to claim 22, wherein the apparatus comprises a product coolingzone downstream of the reaction zone, wherein the gaseous product streamis rapidly cooled in the product cooling zone by injecting a condensateinto the gaseous product stream at multiple points such that thevaporisation of the condensate cools the gaseous product stream.
 25. Theprocess according to claim 22, wherein the temperature of the gaseousproduct stream is reduced to less than 800° C. within 60 ms from exitingthe reaction zone.
 26. The process according to claim 22, wherein theresistance zone has an average inertial pressure gradient coefficient ofbetween 1000-5000/m, preferably between 2000-4000/m, such as between2500-3500/m.
 27. The process according to claim 22, wherein the gaseousparaffinic hydrocarbon is ethane, propane or butane, optionally inadmixture with other hydrocarbons and optionally with other materials,for example methane, nitrogen, carbon monoxide, carbon dioxide, steam orhydrogen.
 28. A process according to claim 22, wherein the ratio of thegaseous paraffinic hydrocarbon to the oxygen-containing gas mixture isfrom 5 to 20 times the stoichiometric ratio of hydrocarbon tooxygen-containing gas for complete combustion to carbon dioxide andwater, preferably from 5 to 10 times the stoichiometric ratio ofhydrocarbon to oxygen-containing gas.
 29. A process according to claim22, wherein the pressure at the first and second inlets is preferablybetween 10-50 barg, most preferably between 20-40 barg, andadvantageously between 25-35 barg.
 30. The process according to claim22, wherein the first supply means comprises at least one first inletfor supplying the oxygen containing gas to at least one first manifoldand a plurality of injection tubes exiting said first manifold fordelivery of the oxygen containing gas, and the second supply meanscomprises at least one second inlet for supplying the gaseous paraffinichydrocarbon to at least one second manifold and a plurality of conduitsexiting said second manifold for delivery of the gaseous paraffinichydrocarbon, wherein the second manifold is positioned downstream of thefirst manifold with respect to the flow of the oxygen containing gas,and the resistance zone is positioned downstream of the second manifoldwith respect to the flow of the oxygen containing gas and the gaseousparaffinic hydrocarbon and is in fluid communication with the conduitsexiting the second manifold, and wherein each conduit comprises anupstream end exiting the second manifold and a downstream end in fluidcommunication with the resistance zone and wherein the injection tubesexiting the first manifold are arranged such that they extend throughthe second manifold and project axially into the upstream end of theconduits, which process comprises passing the oxygen containing gas intothe first manifold and injecting the oxygen-containing gas via theplurality of injection tubes into the plurality of conduits, and passingthe gaseous paraffinic hydrocarbon via the second manifold into theplurality of conduits wherein the gaseous paraffinic hydrocarbon iscontacted in an essentially parallel manner and mixed with theoxygen-containing gas.
 31. The process according to claim 30, which theapparatus also comprises a first cooling zone contacting the downstreamend of the plurality of conduits exiting the second manifold arrangedsuch that the downstream ends of the plurality of conduits are cooled.32. The process according to claim 30, wherein the first manifold is afirst chamber and the second manifold is a second chamber and theinjection tubes exiting the first chamber form a plurality of elongatedpassageways extending through the second chamber into the upstream endof the plurality of conduits exiting the second manifold.
 33. Theprocess according to claim 30, wherein the injection tubes end in anozzle which provides a restriction at the opening, and which preferablyhas an internal diameter in the range between 0.5 to 3.0 mm, such asbetween 1.0 to 2.0 mm.
 34. The process according to claim 30, whereinflow restrictors are provided between the outer surface of the injectiontubes and the inner surface of the conduits, at a location at or closeto where the injection tubes enter the conduits at the upstream end ofthe conduits.
 35. A process according to claim 22, wherein the firstsupply means comprises at least one first inlet for supplying the oxygencontaining gas to at least one first manifold and a plurality of firstinjection tubes exiting said first manifold for delivery of the oxygencontaining gas, and the second supply means comprising at least onesecond inlet for supplying the gaseous paraffinic hydrocarbon to atleast one second manifold and a plurality of second injection tubesexiting said second manifold for delivery of the gaseous paraffinichydrocarbon, wherein each injection tube has an exit at the end remotefrom the manifold and which has a cross-sectional opening of 1 mm² orless, and wherein the exits from the first and second injection tubesare co-located in an intermixed configuration, which process comprises:passing the oxygen containing gas from the least one first inlet via theleast one first manifold to the plurality of the first injection tubesand passing the gaseous paraffinic hydrocarbon from the least one secondinlet via the least one second manifold to the plurality of secondinjection tubes such that the gaseous paraffinic hydrocarbon iscontacted in an essentially parallel manner and mixed with theoxygen-containing gas.
 36. The process according to claim 35, whereinthere are at least 100000 first and second injection tubes in total persquare metre.
 37. The process according to claim 36, wherein there areat least 1000000 first and second injection tubes in total per squaremetre.
 38. The process according to clam 35, wherein the exits from theinjection tubes are all located in an essentially planar configuration.39. The process according to claim 35, wherein each injection tube hasan exit at the end remote from the manifold which has a cross-sectionalopening of 0.5 mm² or less, more preferably 0.2 mm² or less, such as 0.1mm² or less.
 40. The process according to claim 35, wherein theinjection tubes are formed as passageways in a diffusion bonded block.41. Apparatus suitable for reacting a first gaseous reactant with asecond gaseous reactant to form a gaseous product, the apparatus beingas defined in claim
 30. 42. Apparatus suitable for reacting a firstgaseous reactant with a second gaseous reactant to form a gaseousproduct, the apparatus being as defined in claim 35.